1. Field of the Disclosure
The present invention relates to a method and apparatus for analysing three dimensional (3D) video material.
2. Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor implicitly admitted as prior art against the present invention.
Three dimensional (3D) television has recently been made available to the consumer, and it is expected that the amount of 3D equipment and programming will increase rapidly in the next few years.
3D television relies on a stereoscopic technique whereby pairs of images are captured by respective cameras which are laterally displaced (i.e. substantially in a horizontal image direction) by a certain distance, for example a typical spacing of a user's eyes. The pairs of images therefore represent slightly different views of the same scene; in general they will encompass the same items within the scene (except perhaps at the image extremities) but the relative positions of the items between the two images will depend on factors such as the camera alignment and the distance of the items from the camera arrangement.
When the images are displayed, it is important that each of the user's eyes sees (at least mainly) a respective one of the image pair. In practice this is achieved in various ways, such as by the user wearing polarising, time multiplexing or colour-filtering spectacles, or by the television screen itself being provided with a special lens arrangement which diverts each of the two images to a respective eye position of the viewer. Of these, the colour-filtering technique, common in early attempts at 3D cinema, is not generally used in 3D television technology.
Returning to the 3D camera system, each of the pair of images is captured by an independent camera, with its own lens and image capture arrangement (for example a CCD arrangement). But in order to maintain the 3D illusion for the viewer, it is important that the two images of each image pair are closely matched in terms of their image capture properties. Various adjustable parameters are available to the operator of a professional video camera, but the task of setting up a 3D camera arrangement is significantly more difficult than that of setting up a conventional (single) video camera because of the need not only to set the various parameters correctly for the current scene, but also to set the parameters so that the two cameras forming the 3D camera arrangement generate images with identical image properties. In the case of a domestic video camera, the range of adjustments available to the user is much more limited, making it even more difficult to set the two cameras to provide identical image properties.
A further aspect that needs care in 3D video capture is that of the viewer's perception of the video. It is possible for video producers to over-use the 3D effect, particularly by displaying objects (in the 3D video as viewed) so that they appear to be too far in front of the screen. This can cause subjective unpleasantness, or even nausea, for the viewer. Similarly, changes in display depth which are abrupt or simply too rapid can also cause subjective unpleasantness. It has been postulated that this is because the 3D display tricks the human psychovisual system into believing that an object is at a distance from the viewer which is different to the separation between the viewer and the display screen. The viewer's eyes instinctively attempt to focus on the perceived 3D position of an object, particularly as it gets closer to the viewer than the display screen. However, for viewing a 3D video the eyes must of course continue to focus on the plane of the display screen.
This invention provides an image analysis apparatus for processing a 3D video signal comprising successive pairs of images representing different respective views of a scene to generate an image depth indicator; the apparatus comprising:
a correlator configured to correlate image areas in one of the pair of images with image areas in the other of the pair of images so as to detect displacements of corresponding image areas between the two images;
a graphics generator configured to generate a graphical representation of the distribution of the displacements, with respect to a range of possible displacement values, across the pair of images; and
a display generator for generating for display the graphical representation in respect of a current pair of images and in respect of a plurality of preceding pairs of images, so as to provide a time-based representation of variations in the distribution of the displacements.
The invention also provides an image analysis apparatus for processing an image to generate an image focus indicator, the apparatus comprising:
a focus detector configured to detect respective local focus estimates for a plurality of blocks of the image, and to combine the local focus estimates to generate the image focus indicator for that image.
Further respective aspects and features of the invention are defined in the appended claims. It is to be understood that the foregoing general description of the invention and the following details description are exemplary, but are not restrictive, of the invention.